Friday, July 20, 2012

Hunting Snakes Have Patience

After seven weeks of grueling field work, we have completed this year's data collection on squirrel-snake interactions. This year was much different than last year--the lack of rain led to less overall vegetation cover and what appeared to be reduced snake activity. Last year we recorded several strikes on squirrel pups, but we only saw a few this year. In fact, by the time we left BORR, most of the snakes had lost body mass instead of gaining it, suggesting that they still had not successfully found a meal. Eating seems like such a simple task to us, but for snakes, capturing prey is harder than it looks. It may take weeks before a snake is able to eat--snakes must complete three steps to successfully consume a meal: (1) strike and hit the prey, (2) envenomate the prey, and (3) relocate the prey after envenomation.

Our video recordings have shown that snakes can falter at all three steps. We have seen many instances where a snake clearly strikes and hits a prey item, and yet it never searches for it. We suspect that the snake was unable to successfully envenomate the prey, so it was not worth its time to go look for it. We have also seen snakes strike and kill prey, but unable to find the prey afterward. This year we found a squirrel pup that had been envenomated; still alive, but clearly succumbing to the venom. Upon our arrival, the pup ran into the burrow where the snake that struck it was. The snake emerged an hour later looking for the pup. It moved in and out of a triangle of three burrows (NOT the burrow that the pup was actually in) for a total of 5 hours searching for the dead pup. It never found it. It is so interesting that a snake could wait for days just to strike a squirrel and yet, even when it does, it may not relocate it afterward.  

Teetee, male northern Pacific rattlesnake, in ambush right outside a squirrel burrow. It took him 13 days to get a meal.

Although it is tough being a foraging snake, feeding events still occur. Our most exciting feeding event this year was accomplished by Greeata, a female northern Pacific rattlesnake. It only took Greeata 2 days to successfully consume a squirrel pup. Initially, she chose several ambush sites outside of pup burrows at the base of a tree. However, in the end, she managed to strike a pup while underground beneath a log. While radio-tracking her, we found a dead squirrel pup just outside her burrow. We set up a camera on it, and lo and behold two hours later she emerged to consume it. It was quite an exciting day. Below I have posted a video of her selecting her ambush sites, and some pics of her consuming her big meal. Enjoy!

Greeata pulling the dead pup into the shade of her log

She swallows the pup at the entrance of her log burrow